Embodiments of the present invention relate to a chemical mechanical polisher having movable slurry dispensers and related methods.
In the fabrication of the integrated circuits (ICs) and displays, chemical-mechanical planarization (CMP) is used to smoothen the surface topography of a substrate for subsequent etching and deposition processes. A typical CMP polisher comprises a polishing head that oscillates and presses a substrate against a polishing pad while a slurry of abrasive particles is supplied to the polishing pad to polish the substrate. CMP can be used to planarize dielectric layers, deep or shallow trenches filled with polysilicon or silicon oxide, and metal films. It is believed that CMP polishing is a result of both chemical and mechanical effects, for example, a chemically altered layer is repeatedly formed at the surface of the material being polished and then polished away. For example, in metal polishing, a metal oxide layer can be formed and removed repeatedly from the surface of the metal layer during CMP polishing. In oxide polishing, the oxide layer is both chemically and physically eroded by the polishing slurry.
One type of conventional slurry dispenser comprises a fixed arm having a single slurry dispensing nozzle which releases slurry from a fixed point above the polishing pad. The slurry spreads across the polishing pad from the rotary or oscillating motion of the polishing pad and/or substrate carrier. However, because the slurry is dispensed from a single position above the platen, which is often at a mid-point of the radius of the platen, the resultant distribution of slurry across the surface of the platen is not always very uniform. Rotation of the underlying polishing platen and the resultant centrifugal forces causes the slurry to spread radially outward from the median point. However, a preferentially higher concentration of slurry forms in a circular strip that radiates outward from the median dispensing point due to these centrifugal forces, and a lower slurry concentration region forms between the point of dispensation and the radially inner region. This can result in uneven polishing rates across the diameter of the substrate being polished.
Multipoint slurry dispensers also been developed to provide a more uniform distribution of slurry for polishing single substrates, as for example, described in U.S. Pat. No. 6,284,092, entitled “CMP Slurry Atomization Slurry Dispense System”. A sweeping multipoint slurry dispenser has also been used to spread the slurry across the pad, as for example, described in U.S. Pat. No. 7,052,374, entitled “Multipurpose Slurry Delivery Arm for Chemical Mechanical Polishing”. However, while these slurry dispensing systems provide a better slurry distribution for single substrate polishers, they do not provide effective slurry distribution for newer generations of CMP polishers which use multiple carrier heads to polish several substrates at the same time or which are used for polishing large substrates. Thus it is desirable to have a chemical mechanical polisher with a slurry dispensing system that provides a more uniform distribution of slurry across the surface of the polishing pad for simultaneously polishing multiple substrates or for polishing large substrates.